The implication of Streptococcus sanguis in the process of caries formation, and the apparent intimate involvement of the microbial dextran in this process indicates that a thorough investigation of the enzyme responsible for its synthesis should be carried out. Dextran sucrase, an extracellular enzyme which catalyzes the transfer of glucose from sucrose to the growing dextran, is to be investigated, with regard to its mechanism, and the pathway of the reaction it catalyzes. The purpose of these studies is to provide an understanding of the reaction so that a rational approach to controlling the reaction can be made. Two enzymes have been isolated from culture fluids, and in one case has been purified to homogeneity. This enzyme preparation will be used to continue studies on the mechanism of catalysis, on the mode of polymerization, and on the structural characteristics of the enzyme. The formation of a glucosylated enzyme has been shown, and the proposed work will attempt to demonstrate that it is an obligatory intermediate. The nature of the linkage to the protein and the characteristics of the sugars present are to be studied. In addition knowledge of the amino acids at the active site will be sought. Questions concerning the direction in which polymerization occurs will be examined, as well as the basis for multiple types of bonding in the dextrans formed by the purified enzymes, by the utilization of substrate analogs. The subunit structure of the enzyme will be examined under a variety of conditions.